Hydraulically damping rubber bearings are used in the prior art for the damped support of components of a motor vehicle, such as, for example, a guiding link or a front axle of a motor vehicle.
With increasing demands of comfort, the significance of the damping of oscillations produced in a motor vehicle or external oscillations which are transmitted, for example, from the road to the vehicle, is increasing. This is particularly significant as a result of the required reduction of the noise level in the inner space and the reduction of vibrations, which are perceived to be unpleasant. As a result of the positive resilient and damping properties of elastomer materials, elastomer bearings—in this instance also referred to as rubber bearings—are increasingly used, in order, for example, to support the drive unit or movable components in the motor vehicle. The specific composition of the elastomer has a significant influence on the quality and the damping properties. As a result of a change of the material composition of the elastomer, the hardness and the resilience of the bearings can be influenced in a decisive manner. However, a limit is set on this variability where high oscillation amplitudes have to be damped. These are produced, for example, when the drive unit is in idle mode or when movements act in a periodic and abrupt manner on the chassis on an uneven road surface. Damping these so-called resonance oscillations is possible only in a limited manner using conventional elastomer bearings. However, since particularly resonance oscillations are perceived to be very disruptive and very unpleasant in the vehicle and can further bring about damage to cost-intensive components, hydraulically damping elastomer bearings are becoming increasingly widespread in modern motor vehicles. These have at least two chambers which are separated from each other and in which a damping fluid is contained. The chambers are connected to each other by means of a flow channel and are deformed in the event of an external force acting on the elastomer bearing so that damping fluid can pass from one chamber to the other. The chamber walls provide resistance to the shape change which leads to a pressure change in the chambers. A measurement for this pressure change as a result of the volume displacement which is produced thereby is referred to as the “deflection spring rate”. In order to compensate for the pressure difference between the chambers, the chambers are connected to each other by means of the flow channel. In the event of deflection at low frequencies, there is a pressure compensation between the chambers exclusively via this flow channel. Consequently, the elastomer body makes a significant contribution to the resilience and damping of the elastomer bearing in this instance. As the frequency increases, however, a damped system which is capable of oscillation and which comprises the resilient chamber walls and the mass of the damping fluid located in the flow channel becomes increasingly important. If an elastomer bearing becomes excited with hydraulic damping in the region of a resonance frequency, the damping changes and consequently the resilient properties of the elastomer bearing as a whole change. Above the resonance frequency, the inertia of the quantity of fluid in the flow channel and the friction ultimately prevent a further pressure compensation between the chambers. The rigidity of the chamber walls thus supports the carrier rigidity and brings about an increase of the overall rigidity in comparison with low-frequency loads.
The damping action of rubber bearings of the generic type is accordingly based on the principle of a viscous friction damping which is achieved by means of a fluid exchange between at least two fluid chambers which are connected in technical fluid terms within a relevant connection channel, which acts as a flow connection. In this instance, depending on the loading of the rubber bearing between the at least two fluid chambers, a volume of fluid is exchanged, whereby a damping of the bearing is achieved since the fluid volume which can be displaced between the fluid chambers, as a result of the mass inertia thereof and as a result of the fluid resistance, applies a damping action in a flow channel which is required for the fluid exchange. The (frequency) position of the damping maximum is in this instance dependent on the channel or throttle cross-section or the channel or throttle length of the connection or flow channel between the fluid chambers and the configuration of the deflection springs (active face and volume resilience).
In order to comply with specific requirements, it is known, for example, from DE 102 13 627 A1 to provide a flow connection between two fluid chambers which comprises at least two individual connections, of which at least one individual connection can be switched on or off.
Such switchable rubber bearings are consequently capable of preventing a fluid exchange between the fluid chambers, whereby the rigidity of the arrangement is increased. A volume resilience is then produced only via the rubber material of the bearing itself, that is to say, via the chamber walls of the fluid chambers.